1. Technical Field
The present invention relates to a method of manufacturing a decorative molding, more particularly, to a method of manufacturing a large decorative molding having a plurality of spaced-apart surface sections to be decorated.
2. Related Art
Vehicles include a radiator grille, which is placed at the vehicle's front end and functions as an air inlet to supply air to the radiator behind the grille while traveling. To perform this function, radiator grilles are formed to have a louver or a mesh that has gaps serving as the air inlets. Additionally, radiator grilles, which are placed on the front surfaces (the outer periphery surfaces) of vehicles, are required to offer high designabilities. To meet such requirements, decorations are added to the front end (the tip) of a louver or a mesh.
One way to decorate a radiator grille (a resin molding) is to form a decorative layer, by hot stamping, on a surface section to be decorated at the front end of the grille. In hot stamping, a heated pressing member is pressed against a transfer sheet placed on a surface section to be decorated (and thereby applies heat and pressure thereto) to transfer the foil in the transfer sheet to the surface section, thereby forming a decorative layer.
More specifically, hot stamping is a process to press a heated stamping plate (a pressing member) against a component to be decorated having a surface section to be decorated (a grille having no decorative layer) with a transfer sheet interposed therebetween to thermal transfer the foil in the transfer sheet to the surface section to be decorated.
In conventional hot stamping, a pressing section included in a stamping plate (a pressing member) for pressing a surface section to be decorated is made of rubber (an elastic body), which is elastically deformable. As illustrated in FIG. 11, a rubber piece 24 forming the pressing section is recessed in a surface (a pressing surface) 23a of a stamping plate (a pressing member) 23 and is shaped to match the shape of the perimeter of a surface section to be decorated 5a. 
With such conventional hot stamping, forming a decorative layer in a large grille having a size exceeding 400 mm has been difficult.
More specifically, the end of a louver or a mesh in a vehicle grille presents multiple surface sections to be decorated wish intervals (gaps) therebetween. Vehicle grilles having such shapes tend to suffer significant variability in shrinkage depending on conditions, such as dwell pressure and temperature during molding, thereby lowering dimensional accuracy. This leads to a problem that the positions of surface sections to be decorated 5a and 5b are deviated, as illustrated in FIG. 12. In the illustrated case, the position of the surface section to be decorated 5a relative to that of the surface section to be decorated 5b is deviated. This results in misalignment of the surface section to be decorated 5b and a rubber piece 24b when they are brought into contact with each other with the surface section to be decorated 5a and a rubber piece 24a being aligned. Since the rubber piece 24b is shaped to fit the surface section to be decorated 5b, such a misalignment causes difficulty in uniform contact (uniform pressing). Such nonuniform pressure on the surface section to be decorated 5b results in a transfer defect.
The problem of deviated positions for decoration due to the low dimensional accuracy arises particularly in large components to be decorated with an area to be decorated having a size exceeding 400 mm. Vehicle grilles in particular are large components and are susceptible to low dimensional accuracy.
To solve such a problem, a hot stamping process may be performed more than once using a segmented stamping plate while pressing positions are shifted plural times. This approach, however, is problematic in that the increased number of operation processes results in increased manufacturing costs.
As a solution to this, methods have been studied to use just one process to complete hot stamping on a large component to be decorated (molding). For example, one such method is described in JP 2002-166700A.
JP 2002-166700A describes a method in which a thermal transfer foil (a transfer sheet) is put over a large plastic molding (a component to be decorated) and they are brought into contact with each other by removing air by vacuum with their perimeters clamped together. A stamping plate is then moved up and down (and pressed against the molding) add decorations thereto.
The hot stamping method described in JP 2002-166700A, which is directed to a plastic molding like an air conditioner grille, poses difficulty in application to a component, like a vehicle grille, having spaced-apart sections to be decorated (surface sections to be decorated) with gaps therebetween.
More specifically, the existence of multiple and spaced-apart surface sections to be decorated with gaps therebetween presents a problem as described above that the positions of the surface sections to be decorated relative to each other are deviated. No solution is described for such problems in JP 2002-166700A, posing difficulty in the application of the technique described therein.
Moreover, the method described in JP 2002-166700A uses a molded rubber piece shaped to fit the surface section to be decorated 5a and the surface 23a of the stamping plate 23. This rubber piece 24, which is a molding and tends to harden (to have a high hardness) to maintain the molded shape, is less prone to deform while conforming to the surface section to be decorated 5a where the rubber piece 24 and the surface section 5a are misaligned with each other and pressed together.